In: Chemistry
Physical Chemistry
A)The electrolytic conductivity of 0.10 M solution of acetic
acid
is 5.3x 10-5 Scm-1. The cell constant was 0.10 cm-1. Neglecting
activity
coefficient, Calculate the acid dissociation constant (Ka).
(Λmo for acetic acid = 390. S cm2 mol-1)
B)The observed osmotic pressure of 0.1 M acetic acid solution
is
2.45 atm at 25.0 oC. Calculate the Van’t Hoff factor (i) and the
degree of
ionization (α). Compare your value with that obtained from problem
1.
Comment on your answer.
A). electrolytic conductivity, k = 5.3x 10-5 Scm-1
concentration, c = 0.10 M
cell constant = 0.10 cm-1
Λmo for acetic acid = 390. S cm2 mol-1
= 390 - 1.676 x 10-5
= 389.99
degree of dissociation, = Λm / Λmo
= 0.99
Acid dissociation constant, Ka = *c / (1 -
)
= 0.992 * 0.10 / (1 - 0.99)
= 0.09801 / 0.01
= 9.801
Thus, acid dissociation constant, Ka = 9.801
B). Osmotic pressure, = 2.45 atm
concentration, c = 0.1 M
Temperature, T = 25 oC = 298 K
We know that -
2.45 = i*0.1*0.0821*298
2.45 = i*2.446
i = 2.45 / 2.446
i = 1.0
Van't Hoff factor, i = 1.0
Acetic acid ionize as -
Acetic acid ionize into 2 ions.
n = 2
degree of ionization (α) = 0